In U.S. Pat. No. 3,419,303, Dec. 31, 1968, there is disclosed a platform-type underframe or chassis unit adapted to receive thereon an open-bottom body balloon. In that construction hollow side sills extend the full length of the body. The present construction is of the same general platform type but is simpler and easier to manufacture and assemble.
The present construction simplifies the side sill and platform construction by providing simple (non-box section) outwardly channeled main side sills extending the full length of the body over the wheel-well zones, making it simple and easy to secure cross-members and horizontal plates between the main side sills, then to secure a floor pan and associated tunnel structure between the cross-members. Longitudinally spaced vertically bulkheads can then be secured to the outer open sides of the main side sills between wheel-well zones; and an outer inwardly-open channel-shaped auxiliary outer side sill, of a length to be received between wheel-well zones, is secured in mating flanges to the main side sill over the bulkheads. If desired, the space between the main side sill and the outer side sill can be filled with a rigidifying strengthening material, such for example as foamed plastic, either pre-formed or injected.
This construction provides a very rigid strong structure, especially in the door area between wheel-well zones, and permits of a very simple and convenient method of assembly.